Method for cooling and lubricating cutting tools



- Spt. 16, 1958 E. G. WHITE I 2,851,764

METHOD FOR COOLING AND LUBRICATING CUTTING TOOLS 7 Fi led Oct. 24, 1952Osc/u/HOR PUMP 25 51 INVENTOR. Emvzsr 4. WHITE BY W g Fm M United Statm? METHOD FOR COOLING AND LUBRICAI'ING CUTTING TOOL Ernest G. White,Cleveland, hio,-assignOr-to .TheStandand Oil Company, Cleveland, Ohio, acorporation'of Ohio Application October 24, 1952, Serial"No. 316,754

1 Claim. to]. 29-496,)

The present invention relates to cutting methods and of .the :uppercover plate 1 9. The chamber 14 is con- .nected through a flexible tube24 to a liquid pump .25

apparatus and, more particularly, to improvements in cooling of cuttingtools and chip lubrication.

In the cutting of metals, such as on a lathe, planer, threader, etc., ithas long been appreciated that the use of a cutting fluid has the effectof improving the smoothness of the cut surface and of increasing toollife. Many proposals have been made with respect to the manner in whichsuch a cutting operation can be improved, but most of these involvecooling the tool and the work surface and lubricating the relativelymoving parts. All of these involve some method of applying the cuttingfluid to the cutting site. i

The most common method is to permit a stream of fluid to flow over thetool and the work. Other proposals direct a stream of the fluid underpressure from various directions. All of these methods are more or lessadeficient in achieving satisfactory cooling and zlnhrieating in thespace between the tool and the wolf-k, where ade quate lubrication isthe most essential.

Accordingly, it is a primary QbjeOlHQf the -present invention to force acutting liquid to penetrate more effectively to the cutting edge of atool.

In accordance with the invention a continuously replenished volume ofcutting liquid at a moderate hydrostatic pressure is subjected toultrasonic longitudinal vibrations which establish high dynamicpressures in a jet issuing from a chamber. The dynamic pressures forcethe jet into intimate contact with the tool close to the cutting edgethereof.

In order that this invention may be more fully understood, it will nowbe described with reference to the accompanying drawing wherein thesingle figure is a schematic diagram of an embodiment of the invention.

Referring now to the drawing, a rotatable workpiece 11 is shown againstwhich a cutting tool 12 is held by a tool holder 13, which is arrangedby a conventional mechanism (not shown) to be moved toward and away fromthe workpiece 11 and to be translated parallel to the axis of rotationthereof. A chamber 14, adapted to contain cutting liquid, is secured byan adjustable bracket 15 to the tool holder 13 generally beneath thetool 12 and on the side facing the wedge-shaped opening 16 formedbetween the tool andthe work and having the cutting edge 17 as an apex.The chamber 14 may be slid toward or away from the opening 16 and fixedat the most effective distance by a thumbscrew 20. The transverseposition of the chamber 14 may be varied within limits by means ofappropriate slots 32 in the bracket 15 and their associated wing nuts33. Further mechanical adjustments may be provided for if desired.

The chamber 14 in the illustrated form of the invention comprises ahollow cylindrical tube 18 having an upper cover plate 19 and a'baseassembly 21, secured thereto and substantially enclosing the same withthe exception of an aperture 22, which may be provided with one or morenozzles 23 located substantially in the center which draws cuttingliquid from a sump 26 beneath the workpiece 11 and supplies the sameunder pressure to the chamber 14 to maintain the same filled withliquid.

As aresult a stream 27 .of cutting liquid emerges from the nozzle 23 andis directed into the wedge-shaped opening 16. The stream 27 may comprisea sheet of liquid parallel to the cutting edge 17 or it'may be composedof :a plurality of spaced parallel jets. The pressure of the liquidsupplied by the pump 25 need only be such as will direct the stream 27to the tool. The pressure is not critical but systems operating on lowpressure, such as about 50 pounds .per square :inch and under, are moreeconomical to construct and are preferred.

In accordance with a theory advanced to explain the effect of cuttingliquids in increasing tool life, the cutting liquid is vaporized as aresult of the high temperature adjacent the cutting edge. Theheatrequired for vaporization substantially cools the cutting edge andthe vapor passes through minute spaces caused by relative vibrationbetween the tool and the workpiece or by slight irregularities in boththe cutting edge and the work surface. The vapor then condenses on thetop of the tool undereath the .chip 28 that comes from the workpiece inan area where the cutting liquid is most effective in reducing thefrictional resistance to themovement of the-chip.

The apparatus of the present invention .is adapted to obtain intimatecontact between the stream of cutting liquid by the extremely highpressures inherent in ultrasonic longitudinal vibrations which aresuperimposed upon the stream 27. For this purpose a transducer oflongitudinal vibrations is associated with the chamber '14.

The transducer may take the form of an X-cut piezoelectric crystal 29which is supported by an electrically insulating holder 39 forming aportion of the base assembly 21. Both faces of the crystal 29 areconductively coated, the front face being in contact with the liquid inthe chamber 14 and the rear face being supported by the holder 30 whichresists the hydrostatic pressure. The front coating is electricallyconnected to the tube 18 which is maintained at ground potential toavoid shock hazard. The rear coating of the crystal 29 is connected toan oscillator 31 adapted to generate ultrasonic electrical waves, whichexcite corresponding mechanical vibrations in the crystal.

Preferably the distance from the face of the crystal 29 to the innersurface of the cover plate 19 is so related to the wave length of thevibrations in the cutting liquid that the reflections from the plate 19are additive to the motion of the crystal. Under this condition, theabovementioned distance is some whole number of half wave lengths, andthe energy transmitted'into the cutting liquid is maximum.

It is also desirable to concentrate the energy in the direction of theaperture 22 and to avoid as much as possible reflections from the sideof the tube 18. In the usual crystal, the energy is radiated in a beamhaving a solid angle that is directly proportional to the wave lengthand inversely proportional to the transverse dimension of the crystal.Accordingly, a high frequency and a large crystal face are seen to befavorable. A crystal having a concaveface may be employed to focus thevibrations on the aperture 22.

The hydrostatic head tends to dampen the crystal vibrations;consequently the lowest static pressure that still provides anaccurately dirigible stream 27 is most advantageous.

When ultrasonic waves are projected against a boundary, which in thiscase is the apex of the wedge-shaped opening 16, an alternating pressureis produced at the This alternating ation. Likewise a chip guard may beemployed to prevent on the basis of its cooling and lubricatingproperties, little I control is had over the acoustic impedance.However, a high frequency may be selected to provide high pressures.Also, since the square of the amplitude is proportional to the radiatedpower, the power of the oscillator 31 is preferably substantial.Although the alternating motion of the liquid is extremely small, thealternating pressures may readily be made extremely large.

The cutting liquid is thus forced by the ultrasonic alternating pressurepresent in the stream 27 into intimate contact with the tool 12 close tothe cutting edge 17 thereof and through the extremely small clearancebetween the tool and the workpiece to permit lubrication of thetool-chip interface.

It isto be pointed out that according to the findings of the prior art,if the speed of the stream is greater than a certain value, the boilingaction at the apex of the wedgeshaped opening 16 is reduced and the heattransference and lubrication are impaired. Apparently this elfect is aresult of an excessive quantity of cutting liquid in the opening 16. Onthe other hand, a high stream speed has heretofore been proposed as oneWay of achieving the necessary penetration to the vicinity of thecutting edge. These conflictingrcriteria are made substantiallycompatible by employing ultrasonic alternating pressure superimposedupon the moving stream 27 in accordance with the present invention.

It is to be understood that an overhead coolant spray may be provided tocatch the stream of cutting liquid when the tool is not engaged with theworkpiece and to absorb the smoke and vapor generated by the cuttingoperthe chip from intercepting the stream.

While I have described my invention in a preferred embodiment employinga crystal as the source of ultrasonic energy, other means for thispurpose known in the art, such as a magnetostrictor, may be employed.

Although the invention has been disclosed with reference to a simplelathe type of cutting operation, it will be appreciated that it isapplicable to many other types of machine operations such as, forexample, milling wherein the workpiece is stationary and the tool movesrelative thereto.

I claim:

A method of cooling and lubricating cutting tools comprising the stepsof directing a stream of cutting liquid at a pressure of not over poundsper square inch into the wedge-shaped space formed by a workpiece andthe relief angle of a cutting tool so that the stream impingessubstantially on the cutting edge of said tool along the line of itscontact with the workpiece, and inducing ultrasonic longitudinalvibrations within said stream.

References Cited in the file of this patent UNITED STATES PATENTS354,498 Kerchove Dec. 14, 1886 1,789,841 Rennick Jan. 20, 1931 2,452,211Rosenthal Oct. 26, 1948 2,498,737 Holden Feb. 28, 1950 2,578,505 CarlinDec. 11, 1951 2,585,103 Fitzgerald Feb. 12, 1952 2,653,517 Pigott Sept.29, 1953 OTHER REFERENCES Pamphlet, Ultrasonic Fundamentals by S. YoungWhite, reprinted from Audio Engineering Magazine, published by RadioMagazines, Inc., 342 Madison Ave., New York 17, N. Y. Copyright 1949.

1 Text, Ultrasonics by Bergmanpublished by John Wiley & Sons, November1946.

